John 1 records this strong and confident statement as a profound witness of Jesus as Messiah. 

The story is about Jesus calling his early disciples, and them also calling others. It seems at first glance that they really "got it", calling Jesus "the Son of God—the King of Israel!” And yet, we know from the rest of the story that they were regularly confused by Jesus and his actions. It seems possible to acknowledge Jesus as Messiah and simultaneously misunderstand most of what he is trying to achieve. That's worth pondering.